An artificial blood vessel is used as a substitute for a blood vessel of a living organism when there is an injury or a disease of the circulatory system. As examples of artificial blood vessels that have recently been attracting attention, there are hybrid artificial blood vessels in which a collagen, a gelatin, an elastin, a fibronectin, etc. is incorporated into a synthetic polymer material and this is then seeded with cells. These hybrid artificial blood vessels have the problem that the cells are susceptible to being detached by rapid blood flow. Furthermore, there is a problem with biocompatibility since the material forming the substrate is a synthetic polymer, and when an artificial blood vessel having a diameter of 3 mm or less is prepared and grafted, it is necessary to continue to take an anticoagulant in order to prevent the intravascular lumen from being narrowed by a blood clot. Furthermore, there is the problem that, when this artificial blood vessel is grafted during a period of growth, it is necessary to graft an artificial blood vessel again by surgery accompanying the growth.
As the synthetic polymer used as the substrate for these hybrid artificial blood vessels, a stretched porous (expanded) polytetrafluoroethylene (e-PTFE) is currently dominant, and this polymer is excellent in terms of non-tackiness and flexibility, but has a problem with strength, and is used only for veins or small arteries (inner diameter 4 to 8 mm). As described above, since synthetic polymers have problems, biopolymers have been attracting attention as materials that can replace the synthetic polymers. Among biopolymers, collagens are present in large amounts in living organisms (occupying about ⅓ of the protein in a living organism) and have biocompatibility and cell-adhesion properties; preparation of an artificial blood vessel using a collagen has been attempted, but one formed from 100% collagen has a problem with strength.
Forming a medical material using a combination of a collagen and a water-soluble elastin is also known, as described later. Elastins are proteins that are present together with collagens in connective tissue such as the dermis of the skin, ligaments, tendons, and vascular wall of an animal and, in particular, a mammal. Elastins are usually present in a living organism as insoluble protein having a three-dimensional net structure. It is well known that hydrolyzing such an elastin with an acid or an alkali or treating it with an enzyme enables the above-mentioned water-soluble elastin to be obtained. Since a water-soluble elastin has the ability to retain a large amount of moisture, it is used as a cosmetic, in particular as a moisturizing agent, and also, together with a collagen, as a health food due to its cosmetic effects such as giving the skin elasticity.
Furthermore, with regard to the water-soluble elastin, a molding composition obtained by mixing a water-soluble elastin and a solubilized collagen (Patent Document 1) or provision of a collagen layer on an inner wall face of an artificial blood vessel substrate and crosslinking this with a water-soluble elastin using a crosslinking agent (Patent Document 2) have been proposed. Moreover, use of a mixture of a crosslinked elastin and a biopolymer such as a collagen as a medical material has been proposed (Patent Document 3). However, an artificial blood vessel, etc. that can withstand practical use has not been developed. Furthermore, the present inventors have proposed a method for obtaining a water-soluble elastin (Patent Document 4).